The Physical Mesomechanics of the Earthquake Source

This paper is a brief review of the main recent results obtained by studying fault slip processes. The published hypotheses and data are analyzed within the approach proposed by Panin, according to which the subsurface is considered as a multilevel hierarchically organized system where all processes evolve consistently at the nano-, micro-, meso- and macroscale levels. The review focuses on the hierarchy of structures that, according to modern concepts, form the seismogenic fault slip zone. The relationship of the structures with the mechanical characteristics of localized slip surfaces and microcontacts determining the slip dynamics of fault zones at the macrolevel is discussed. It is shown that the evolution of the contact properties of filler particles in the slip zone determines not only the occurrence of instability, but also the ability of a fault to recover strength with time. The simplest scheme of the hierarchy of macroscopic asperities is described to support the important principle that the initiation, evolution and arrest of a seismogenic fault depend on the size and relative position of regions with different dynamics of frictional characteristics during slip. The performed analysis of the results of field observations shows that because of the insufficient accuracy of observations and the ambiguous interpretation of the inverse problem solution, it is impossible to correctly identify fault segments with the velocity weakening property. The size and location of these zones can be more accurately determined from the analysis of records of high-frequency oscillations in the vicinity of an earthquake rupture. The basic principles of physical mesomechanics provide a good basis for the interpretation of such results.